Two primary video format standards are utilized worldwide to record, transmit, and display composite video data, namely, the National Television Systems Committee (NTSC) and the Phase Alternating Line (PAL) standards. Both the NTSC and PAL standards define interlaced video systems in which one frame of display pixels is partitioned into alternating interlaced fields, with each interlaced field updated at twice the update rate of the frame. Additionally, many digital versatile disk (DVD) players, DVD player-recorders, and similar video recording and playback systems, output data in an interlaced format, depending on the format used to record the given playback media.
On the other hand, many state of the art display systems, such as high definition television (HDTV) sets, generate displays using a progressive scan format. In the progressive scan format, video data are transmitted and displayed in frames which are not partitioned into fields. In other words, each display frame is generated by sequentially scanning through the lines of each frame at the original field update rate. Hence, in order to interface an interlaced video source, such as television cable interface or a DVD player playing-back an interlaced DVD, with a progressive-scan display system, such as a HDTV set, deinterlacing must be performed.
The 3:2 pulldown technique is typically utilized to convert film into interlaced NSTC video, for example during recording onto DVD or during television broadcast. Generally, film is generated with a frame rate of twenty four (24) frames per second. On the other hand, frames of interlaced NTSC video are generated at a rate of thirty (30) frames per second from odd and even fields having an update rate of approximately sixty (60) fields per second. Hence, 3:2 pulldown compensates for differences between the film frame rate and the NTSC frame rate essentially by generating ten (10) interlaced fields for every four (4) frames of film.
In particular, during 3:2 pulldown, every other frame of film generates three (3) interlaced fields and the intervening frames generate two (2) interlaced fields. For example, if a given frame of film generates three (3) interlaced fields in the sequence odd, even, odd, then the next frame generates two (2) interlaced fields in sequence even, odd, the following frame generates three (3) interlaced fields in the sequence even, odd, even, and so on.
Occasionally, during the video production, processing errors are made during editing, such that the 3:2 sequence of fields is broken. When such a break is reached during progressive scan playback, the processing system generating the progressive scan display must detect the break from the 3:2 sequence and compensate for any resulting display artifacts.
Current progressive scan display processors have the capability to detect breaks in a 3:2 video sequence. However, typically existing out-of-sequence detection techniques are subject to a significant latency, typically up to four (4) frames. During this latency period, unacceptable visible artifacts are generated in the display. Additionally, while it is possible to delay the output stream by four (4) frames, such that these artifacts can be removed, implementing such a delay is expensive in terms of both bandwidth and memory.
Given the increasing popularity of progressive scan display systems for playing back films from 3:2 interlaced data, improved techniques for required for detecting breaks in the 3:2 sequence are required, as well as efficient techniques for continuing to generate an artifact-free progressive scan display after out-of-sequence detection.
Given increasing popularity of progressive scan display systems, as well as the need to maintain compatibility with systems generating interlaced display data, new deinterlacing techniques are required. In particular, these deinterlacing techniques should allow for the generating of progressive scan displays from interlaced data created by 3:2 pulldown.